From: Kuniyuki Iwashima kuniyu@amazon.co.jp
commit c89dffc70b340780e5b933832d8c3e045ef3791e upstream.
Receiving ACK with a valid SYN cookie, cookie_v4_check() allocates struct request_sock and then can allocate inet_rsk(req)->ireq_opt. After that, tcp_v4_syn_recv_sock() allocates struct sock and copies ireq_opt to inet_sk(sk)->inet_opt. Normally, tcp_v4_syn_recv_sock() inserts the full socket into ehash and sets NULL to ireq_opt. Otherwise, tcp_v4_syn_recv_sock() has to reset inet_opt by NULL and free the full socket.
The commit 01770a1661657 ("tcp: fix race condition when creating child sockets from syncookies") added a new path, in which more than one cores create full sockets for the same SYN cookie. Currently, the core which loses the race frees the full socket without resetting inet_opt, resulting in that both sock_put() and reqsk_put() call kfree() for the same memory:
sock_put sk_free __sk_free sk_destruct __sk_destruct sk->sk_destruct/inet_sock_destruct kfree(rcu_dereference_protected(inet->inet_opt, 1));
reqsk_put reqsk_free __reqsk_free req->rsk_ops->destructor/tcp_v4_reqsk_destructor kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1));
Calling kmalloc() between the double kfree() can lead to use-after-free, so this patch fixes it by setting NULL to inet_opt before sock_put().
As a side note, this kind of issue does not happen for IPv6. This is because tcp_v6_syn_recv_sock() clones both ipv6_opt and pktopts which correspond to ireq_opt in IPv4.
Fixes: 01770a166165 ("tcp: fix race condition when creating child sockets from syncookies") CC: Ricardo Dias rdias@singlestore.com Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.co.jp Reviewed-by: Benjamin Herrenschmidt benh@amazon.com Reviewed-by: Eric Dumazet edumazet@google.com Link: https://lore.kernel.org/r/20210118055920.82516-1-kuniyu@amazon.co.jp Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_ipv4.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1503,6 +1503,8 @@ struct sock *tcp_v4_syn_recv_sock(const tcp_move_syn(newtp, req); ireq->ireq_opt = NULL; } else { + newinet->inet_opt = NULL; + if (!req_unhash && found_dup_sk) { /* This code path should only be executed in the * syncookie case only @@ -1510,8 +1512,6 @@ struct sock *tcp_v4_syn_recv_sock(const bh_unlock_sock(newsk); sock_put(newsk); newsk = NULL; - } else { - newinet->inet_opt = NULL; } } return newsk;